Place garlic and salt in a food processor fitted with a metal blade, or in a blender. Pulse for 2 seconds. Add the egg yolk and lemon juice, and pulse on and off until blended. Turn on and begin adding the olive oil (pure first, then extra-virgin) in a thin stream. If it becomes too thick, thin it out with some room-temperature water and continue adding oil until you've used it all. Finish with pepper and (if necessary) a bit more salt.
The reason for using 2/3 pure olive oil is to keep the flavor of the oil from becoming overpowering. This is a perfect example of how by using a fully-flavored extra virgin oil you can use much less, thereby saving money and getting better flavor.
*RAW EGG WARNING
Food Network Kitchens suggest caution in consuming raw and lightly-cooked eggs due to the slight risk of Salmonella or other food-borne illness. To reduce this risk, we recommend you use only fresh, properly-refrigerated, clean, grade A or AA eggs with intact shells, and avoid contact between the yolks or whites and the shell.